1. Field of the Invention
The present invention relates to a roll medium holding unit that holds a roll medium formed by winding a long sheet. The present invention also relates to a roll sheet feeder that uses the roll medium holding unit, and to an image forming apparatus that has the roll medium holding unit.
2. Description of the Related Art
Some image forming apparatuses use roll sheets (roll media) formed by winding long sheets as recording media. Such an image forming apparatus has a roll medium conveyance device that conveys a roll sheet fed out from a roll medium. In the roll medium conveyance device, however, the roll sheet may be obliquely moved or wrinkled due to slack or the like occurring when it is conveyed. In order to prevent such trouble, some roll medium conveyance devices have a mechanism that drives the roll sheet itself in a rewinding direction to apply appropriate tension to the roll sheet.
To this end, some roll medium conveyance devices have a roll medium holding unit having a holding member (referred to as a flange) arranged inside the core pipe of a roll sheet, and rotates and drives a roll sheet through the flange to control the rotation of the roll sheet. By transmitting a driving force to the roll sheet through the holding member of the roll medium holding unit, the roll medium conveyance device can apply tension to the roll sheet and perform rotation control such as the rewinding operation of the roll sheet.
However, the inner diameter of the core pipe of a roll sheet circulating on the market is not standardized and is different depending on manufacturers or the like. Therefore, in order to match the inner diameter of the core pipe of a roll sheet and the attachment diameter of a holding member to each other, an adapter is separately attached to the shaft core of the holding member or a support member provided in the core part of the holding member is shifted in the radius direction of the roll sheet to change the outer diameter of the core part.
Patent Document 1 describes a holding unit that has a separate adapter at the core part of a holding member to change the inner diameter of the core part.
Further, Patent Document 2 describes a device in which the core part of a holding member shifts a rib, which supports the inner peripheral surface of a roll sheet, in a radius direction with a cam.
The holding unit described in Patent Document 1 is simple in configuration because the adapter is only provided in the core part of the holding member. However, handling of the holding unit is complicated because the adapter is separately attached to the holding unit.
Further, the device described in Patent Document 2 requires a locking mechanism or the like in order to reliably replace a supporting member, which gives rise to a problem that the configuration of the device becomes complicated.
Moreover, in roll sheet feeders that feed roll sheets used as recording media in recent large-sized image forming apparatuses, if slack, looseness, or the like occur in the roll sheets when they are conveyed, the roll sheet are likely to be obliquely moved or wrinkled. Therefore, it is necessary to apply appropriate tension to the roll sheets.
To this end, some roll sheet feeders have a mechanism that transmits a driving force in a rewinding direction. Currently, a mainstream technique for transmitting such a driving force includes making a lengthy shaft member (spool) pass through a roll sheet, installing a holding member (flange) as a connection to a core pipe so as to rotate and hold the roll sheet, and transmitting the driving force through the spool and the flange. Thus, the known roll sheet feeders perform rotation control such as application of tension to the roll sheet and a rewinding operation.
However, it is necessary to fix the flange to the shaft of the spool because the width of the roll sheet is made different depending on the size of an image to be recorded. In order to reduce thrust backlash between the flange and the spool, known techniques employ a mechanism that locks an elastic member so as to fix the flange to the spool or the like.
However, the employment of the mechanism that locks the elastic member gives rise to a problem that it additionally requires a locking mechanism. Patent Document 3 discloses an invention that has an elastic member provided in a flange so as to fix the flange to a spool and makes it possible to install even a roll sheet having a different inner diameter while restricting the axis line directions of the spool and the flange. However, the invention still cannot solve the problem in that it employs the mechanism that fixes the elastic member and additionally requires the locking mechanism.
Patent Document 1: JP-B2-3928705
Patent Document 2: JP-A-2009-173428
Patent Document 3: JP-A-2000-095397
Patent Document 4: JP-B2-3772057